Pressure Wave Tool For Unconventional Well Recovery

ABSTRACT

A method is disclosed for selectively fracturing a formation in order to enhance recovery of hydrocarbons from unconventional reservoirs. The method includes generating a pressure wave having a frequency substantially in a resonant frequency range of a geological formation. The pressure wave is transmitted at a targeted location of the formation. A fluid may then be injected into the wellbore at a pressure that causes the fluid to enter any fractures resulting from the pressure wave.

BACKGROUND

Hydrocarbon recovery may be categorized as conventional recovery and unconventional recovery. Conventional recovery includes the process of pumping the hydrocarbons from reservoirs that may be located in permeable subsurface formations such as sand or sandstone.

After decades of recovery operations, conventional recovery in North America is becoming more difficult and unconventional recovery is being used. Unconventional recovery is the recovery of the hydrocarbons from less porous subsurface formations such as shale or other rock. Unconventional recovery of hydrocarbons is more difficult than conventional recovery and uses different techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram of a pressure wave tool apparatus for generating pressure waves into a subsurface formation, according to various embodiments.

FIG. 2 is a diagram of an active antenna array signal transmission, according to various embodiments.

FIG. 3 is a cross-sectional diagram of a wellbore into which a fluid has been injected, according to various embodiments.

FIG. 4 is a flowchart of a method for unconventional reservoir recovery, according to various embodiments.

FIG. 5 is a diagram showing a drilling system, according to various embodiments.

FIG. 6 is a diagram showing a wireline system, according to various embodiments.

FIG. 7 is a block diagram of an example system operable to implement the activities of disclosed methods, according to various embodiments.

DETAILED DESCRIPTION

Some of the challenges noted above, as well as others, may be addressed by creating microfractures in subsurface formations using pressure waves at a frequency that is in a target formation's resonant frequency range. A fluid may then be injected into the fractured formation in order to produce larger pore sizes in the rock. The hydrocarbons may then be recovered from the formation.

FIG. 1 is a cross-sectional diagram of a pressure wave tool apparatus 100 for generating pressure waves into a subsurface formation, according to various embodiments. This tool 100 is for purposes of illustration only as other tools may be used to produce substantially the same results.

The tool 100 is illustrated as being part of a wireline operation. The tool 100 is shown lowered into a cased 136 and cemented 135 borehole 130 in a formation 150. However, as shown and described subsequently, the tool 100 may be incorporated into a drillstring and used during a drilling operation. In such an operation, the borehole 130 may not be cased and cemented.

The tool 100 includes one or more pressure wave generators 110-117 that may produce pressure waves at a frequency that is in a resonant frequency range of the formation 150. The pressure wave generators 110-117 may be individual elements located on the tool body 101. In another embodiment, the pressure wave generators 110-117 may encircle the tool body 101.

The pressure waves may be sound waves produced by sound wave generators 110-117 (e.g., antennas). In another embodiment, the pressure waves may be fluid waves produced by fluid wave generators 110-117 that vibrate the fluid at a resonant frequency that is within the range of resonant frequencies of the formation 150. The fluid may be circulated from the surface through tubing or the drillstring. The pressure waves may have a frequency in a range of approximately 4 kilohertz (kHz) to 6 kHz. Other embodiments may use other frequency ranges depending on the characteristics of the formation.

In operation, the tool 100 is lowered into the wellbore 130. If the pressure wave generators 110-117 are individual elements, the tool 100 may be rotated to cause the elements 110-117 to transmit the pressure waves into the formation substantially surrounding the wellbore 130. If the pressure wave generators 110-117 encircle the tool body 101 or the individual elements 110-117 are located around the tool body 101, the rotation may not be necessary since the pressure waves could be transmitted omnidirectionally.

If the tool 100 is lowered into a cased wellbore 130, it is possible that the pressure wave may damage the casing 136 and/or the cement 135 surrounding the casing. In such an embodiment, the resonant frequencies for these wellbore elements may be avoided to reduce the damage.

FIG. 2 is a diagram of an active antenna array signal transmission, according to various embodiments. This antenna array is only for purposes of illustration of beamforming of the pressure waves. The pressure waves may be transmitted without using beamforming.

The concept illustrated in FIG. 2 uses multiple transmitting antenna elements 200-203 that are coupled to and controlled by a control circuit 250. In an embodiment, the antenna elements 200-203 may be examples of the pressure wave generators 110-117 of FIG. 1.

The control circuit 250 may perform beamforming with the antenna elements 200-203 to change the directionality of the array when transmitting a pressure wave (e.g., sound signal). The control circuit 250 acts as a beamformer to control the phase and relative amplitude of a transmitted signal 210-213 at each respective transmitting antenna 200-203. This phase and relative amplitude control results in a transmitted pattern of constructive and destructive interference of the transmitted signals 210-213 to form the resulting wavefront 230. The beamforming may be used to focus the wavefront 230 as a directional pressure wave to directionally fracture the formation in targeted locations.

FIG. 3 is a cross-sectional diagram of a wellbore 301 into which a fluid 300 has been injected, according to various embodiments. The wellbore in the illustrated embodiment has already been exposed to one or more pressure waves from the pressure wave tool of FIG. 1. Thus, the pores of the formation have been enlarged by the pressure waves to permit the injection of a fluid to expand the pore throat and adsorb to kerogen. The fluid may be any fluid that can adsorb to kerogen in the formation.

The fluid 300 injected into the wellbore 301 may be a gas (e.g., CO₂) or a liquid. The fluid 300 may be injected into the wellbore 301 under pressure that is high enough to force the fluid 300 into the perforation clusters 310, 311 resulting from the pressure wave of the pressure wave tool 100. The fluid 300 may be injected into the wellbore at or above the fracture gradient. The fluid may displace other particles, adsorb to kerogen in the formation, and liberate the hydrocarbons from an unconventional well.

FIG. 4 is a flowchart of a method for unconventional reservoir recovery, according to various embodiments. This method may be executed during a wireline operation or a drilling operation. One or more steps of the method may be performed by a control circuit coupled to the pressure wave tool apparatus, as described subsequently.

In block 401, a resonant frequency range of a geological formation is determined. This may be accomplished using sonic logging tools, in a wireline operation, that transmit sound or pressure waves into the formation and determine the resonant frequency range in response to the signals returned from the formation.

For example, fast formations and smaller wellbores favor higher resonant frequency ranges while slow formations and larger wellbores favor lower resonant frequency ranges (as compared to the higher resonant frequency ranges). A fast formation may be defined as a formation where the velocity of a compressional wave traveling through the wellbore fluid is less than the velocity of a shear wave through the surrounding formation. A slow formation may be defined as the compressional wave velocity being greater than the shear wave velocity.

The resonant frequency range of the formation may also be determined using a microphone at the drill bit. For example, with a microphone directly behind the drill bit, the sound of the rock destruction may provide the ability to estimate the rock properties (e.g., strength, brittleness) and, thus, the resonant frequencies of a formation that comprise rocks having such properties.

Referring again to FIG. 4, the pressure wave tool is lowered or run into the wellbore in the formation. In an embodiment, the wellbore may be a cemented, perforated hole. In another embodiment, the wellbore may be formed by a drilling operation substantially concurrently with operation of the pressure wave tool. In block 403, at least one pressure wave is generated that has a frequency substantially in a resonant frequency range of the geological formation into which the tool is inserted. The generated frequency may be in a range that avoids the resonant frequency of the cement in the wellbore.

In block 405, the generated pressure wave is directed at a targeted location of the formation. This may be accomplished by either transmitting the pressure wave substantially omnidirectionally from the tool or by using beamforming to focus the pressure wave at a particular location of the formation. The beamforming may be the result of the control circuit adjusting the phase and/or amplitude of a signal transmitted from each of a plurality of antenna elements to beamform the pressure wave to target the targeted location.

In block 407, a fluid is injected into the wellbore at a pressure that causes the fluid to enter any fractures resulting from the pressure wave. The fluid may injected as a gas (e.g., carbon dioxide) or as a liquid. The fluid may be injected at or above the fracture gradient resulting from the pressure wave directed at the targeted location.

FIG. 5 is a diagram showing a drilling system, according to various embodiments. The system 564 includes a drilling rig 502 located at the surface 504 of a well 506. The drilling rig 502 may provide support for a drillstring 508. The drillstring 508 may operate to penetrate the rotary table 510 for drilling the borehole 512 through the subsurface formations 590. The drillstring 508 may include a drill pipe 518 and the bottom hole assembly (BHA) 520 (e.g., drillstring), perhaps located at the lower portion of the drill pipe 518.

The BHA 520 may include drill collars 522, a down hole tool 524, stabilizers, sensors, an RSS, a drill bit 526, as well as other possible components. For example, the BHA 520 may include the pressure wave tool apparatus 100 of FIG. 1. The drill bit 526 may operate to create the borehole 512 by penetrating the surface 504 and the subsurface formations 590.

During drilling operations within the cased borehole 512, the drillstring 508 (perhaps including the drill pipe 518 and the BHA 520) may be rotated by the rotary table 510. Although not shown, in addition to or alternatively, the BHA 520 may also be rotated by a motor (e.g., a mud motor) that is located down hole. The drill collars 522 may be used to add weight to the drill bit 526. The drill collars 522 may also operate to stiffen the bottom hole assembly 520, allowing the bottom hole assembly 520 to transfer the added weight to the drill bit 526, and in turn, to assist the drill bit 526 in penetrating the surface 504 and subsurface formations 590.

During drilling operations, a mud pump 532 may pump drilling fluid (sometimes known by those of ordinary skill in the art as “drilling mud”) from a mud pit 534 through a hose 536 into the drill pipe 518 and down to the drill bit 526. The drilling fluid can flow out from the drill bit 526 and be returned to the surface 504 through an annular area 540 between the drill pipe 518 and the sides of the borehole 512. The drilling fluid may then be returned to the mud pit 534, where such fluid is filtered. In some examples, the drilling fluid can be used to cool the drill bit 526, as well as to provide lubrication for the drill bit 526 during drilling operations. Additionally, the drilling fluid may be used to remove subsurface formation cuttings created by operating the drill bit 526.

A workstation 592 including a control circuit 596 (i.e., controller) may include modules comprising hardware circuitry, a processor, and/or memory circuits that may store software program modules and objects, and/or firmware, and combinations thereof. The workstation 592 may also include modulators and demodulators for modulating and demodulating data transmitted downhole or received from the downhole environment. The workstation 592 and controller 596 are shown near the rig 502 only for purposes of illustration as these components may be located at remote locations or in the BHA 520.

These implementations can include a machine-readable storage device having machine-executable instructions, such as a computer-readable storage device having computer-executable instructions. Further, a computer-readable storage device may be a physical device that stores data represented by a physical structure within the device. Such a physical device is a non-transitory device. Examples of a non-transitory computer-readable storage medium can include, but not be limited to, read only memory (ROM), random access memory (RAM), a magnetic disk storage device, an optical storage device, a flash memory, and other electronic, magnetic, and/or optical memory devices.

FIG. 6 is a diagram showing a wireline system 664, according to various examples of the disclosure. The system 664 may comprise a wireline logging tool body 620, as part of a wireline logging operation in a cased and cemented borehole 512, that includes the pressure wave tool apparatus 100 as described previously.

A drilling platform 586 equipped with a derrick 588 that supports a hoist 690 can be seen. Drilling oil and gas wells is commonly carried out using a string of drill pipes connected together so as to form a drillstring that is lowered through a rotary table 510 into the cased borehole 512. Here it is assumed that the drillstring has been temporarily removed from the borehole 512 to allow the wireline tool 620 that includes the pressure wave tool 100 to be lowered by wireline or logging cable 674 (e.g., slickline cable) into the borehole 512. Typically, the wireline logging tool body 620 is lowered to the bottom of the region of interest and subsequently pulled upward at a substantially constant speed.

During the upward trip, at a series of depths, various instruments may be used to perform measurements to determine a frequency range for the resonant frequency of the formation 590. The wireline data may be communicated to a surface logging facility (e.g., workstation 592) for processing, analysis, and/or storage. The workstation 592 may have a controller 596 that is coupled to the pressure wave tool 100 through the wireline 674 or telemetry in order to control beamforming of signals transmitted from the tool 100.

FIG. 7 is a block diagram of an example system 700 operable to implement the activities of disclosed methods, according to various examples of the disclosure. The system 700 may include a tool housing 706 having the pressure wave tool 100 such as that illustrated in FIG. 1. The system 700 may be configured to operate in accordance with the teachings herein to perform beamforming and fracturing of the formation 590. The system 700 of FIG. 7 may be implemented as shown in FIGS. 5 and 6 with reference to the workstation 592 and controller 596.

The system 700 may include a controller 720, a memory 730, and a communications unit 735. The controller 720, the memory 730, and the communications unit 735 may be arranged to operate as a control circuit to control operation of the pressure wave tool 100 and execute any methods disclosed herein.

The communications unit 735 may include downhole communications for appropriately located sensors in a wellbore. Such downhole communications can include a telemetry system. The communications unit 735 may use combinations of wired communication technologies and wireless technologies at frequencies that do not interfere with on-going measurements.

The system 700 may also include a bus 737, where the bus 737 provides electrical conductivity among the components of the system 700. The bus 737 can include an address bus, a data bus, and a control bus, each independently configured or in an integrated format. The bus 737 may be realized using a number of different communication mediums that allows for the distribution of components of the system 700. The bus 737 may include a network. Use of the bus 737 may be regulated by the controller 720.

The system 700 may include display unit(s) 760 as a distributed component on the surface of a wellbore, which may be used with instructions stored in the memory 730 to implement a user interface to monitor the operation of the tool 100 or components distributed within the system 700. Such a user interface may be operated in conjunction with the communications unit 735 and the bus 737. Many examples may thus be realized. A few examples of such examples will now be described.

Example 1 is a method comprising: generating a pressure wave having a frequency substantially in a resonant frequency range of a geological formation; directing the pressure wave at a targeted location of the formation; and injecting a fluid into the wellbore at a pressure that causes the fluid to enter fractures resulting from the pressure wave.

In Example 2, the subject matter of Example 1 can further include determining the resonant frequency range of the formation in response to a wireline operation.

In Example 3, the subject matter of Examples 1-2 can further include wherein injecting the fluid comprises injecting a gas into the wellbore.

In Example 4, the subject matter of Examples 1-3 can further include wherein injecting the fluid comprises injecting a fluid that adsorbs to kerogen.

In Example 5, the subject matter of Examples 1-4 can further include wherein injecting the fluid comprises injecting the fluid at or above a fracture gradient resulting from directing the pressure wave at the targeted location.

In Example 6, the subject matter of Examples 1-5 can further include wherein directing the pressure wave at the targeted location comprises directing the pressure wave from an active array antenna comprising a plurality of antenna elements.

In Example 7, the subject matter of Examples 1-6 can further include further comprising adjusting a phase and/or amplitude of a signal transmitted from the plurality of antenna elements to beamform the pressure wave to target the targeted location.

In Example 8, the subject matter of Examples 1-7 can further include wherein directing the pressure wave comprising directing the pressure wave from a pressure wave tool comprising a plurality of pressure wave generators.

Example 9 is a tool apparatus comprising: a tool body configured to be lowered into a borehole of a geological formation; and at least one pressure wave generator located on the tool body, the at least one pressure wave generator configured to transmit pressure waves at a resonant frequency of the geological formation.

In Example 10, the subject matter of Example 9 can further include wherein the at least one pressure wave generator comprise a plurality of antenna elements.

In Example 11, the subject matter of Examples 9-10 can further include wherein the plurality of antenna elements comprise an active antenna array configured to produce a beamformed pressure wave.

In Example 12, the subject matter of Examples 9-11 can further include a control circuit coupled to the plurality of antenna elements, the control circuit configured to control a phase and/or amplitude of a signal from each of the plurality of antenna elements to generate the beamformed pressure wave.

In Example 13, the subject matter of Examples 9-12 can further include wherein the control circuit is further configured to avoid generating resonant frequencies of cement.

In Example 14, the subject matter of Examples 9-13 can further include wherein the at least one pressure wave generator comprises a plurality of individual antenna elements located around the tool body.

Example 15 is a system comprising: a rig to support a drillstring or a wireline tool; a control circuit configured to execute beamforming; and a pressure wave tool apparatus located in either the drillstring or the wireline tool and coupled to the control circuit, the apparatus comprising: a tool body; and a plurality of pressure wave generators disposed around the tool body and configured to transmit a targeted pressure wave in response to the beamforming by the control circuit.

In Example 16, the subject matter of Example 15 can further include wherein the control circuit is configured to control an amplitude and/or a phase of a signal transmitted from each antenna element such that the targeted pressure wave is at a frequency that avoids a resonant frequency of cement.

In Example 17, the subject matter of Examples 15-16 can further include wherein the plurality of pressure wave generators comprise a plurality of sound wave generators.

In Example 18, the subject matter of Examples 15-17 can further include wherein the plurality of pressure wave generators comprise a plurality of fluid wave generators.

In Example 19, the subject matter of Examples 15-18 can further include wherein the plurality of fluid wave generators are configured to vibrate a fluid at a frequency that is within a range of resonant frequencies of a formation.

In Example 20, the subject matter of Examples 15-19 can further include wherein a frequency of the targeted pressure wave is in a range of resonant frequencies of a target formation, wherein the range of resonant frequencies is determined based on wireline sonic logging tools or a microphone at a drill bit.

Although specific examples have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific examples shown. Various examples use permutations and/or combinations of examples described herein. It is to be understood that the above description is intended to be illustrative, and not restrictive, and that the phraseology or terminology employed herein is for the purpose of description. Combinations of the above examples and other examples will be apparent to those of skill in the art upon studying the above description. 

What is claimed is:
 1. A method comprising: generating a pressure wave having a frequency substantially in a resonant frequency range of a geological formation; directing the pressure wave at a targeted location of the formation; and injecting a fluid into the wellbore at a pressure that causes the fluid to enter fractures resulting from the pressure wave.
 2. The method of claim 1, further comprising determining the resonant frequency range of the formation in response to a wireline operation.
 3. The method of claim 1, wherein injecting the fluid comprises injecting a gas into the wellbore.
 4. The method of claim 1, wherein injecting the fluid comprises injecting a fluid that adsorbs to kerogen.
 5. The method of claim 1, wherein injecting the fluid comprises injecting the fluid at or above a fracture gradient resulting from directing the pressure wave at the targeted location.
 6. The method of claim 1, wherein directing the pressure wave at the targeted location comprises directing the pressure wave from an active array antenna comprising a plurality of antenna elements.
 7. The method of claim 6, further comprising adjusting a phase and/or amplitude of a signal transmitted from the plurality of antenna elements to beamform the pressure wave to target the targeted location.
 8. The method of claim 1, wherein directing the pressure wave comprising directing the pressure wave from a pressure wave tool comprising a plurality of pressure wave generators.
 9. A tool apparatus comprising: a tool body configured to be lowered into a borehole of a geological formation; and at least one pressure wave generator located on the tool body, the at least one pressure wave generator configured to transmit pressure waves at a resonant frequency of the geological formation.
 10. The tool apparatus of claim 9, wherein the at least one pressure wave generator comprises a plurality of antenna elements.
 11. The tool apparatus of claim 10, wherein the plurality of antenna elements comprise an active antenna array configured to produce a beamformed pressure wave.
 12. The tool apparatus of claim 11, further comprising a control circuit coupled to the plurality of antenna elements, the control circuit configured to control a phase and/or amplitude of a signal from each of the plurality of antenna elements to generate the beamformed pressure wave.
 13. The tool apparatus of claim 12, wherein the control circuit is further configured to avoid generating resonant frequencies of cement.
 14. The tool apparatus of claim 9, wherein the at least one pressure wave generator comprises a plurality of individual antenna elements located around the tool body.
 15. A system comprising: a rig to support a drillstring or a wireline tool; a control circuit configured to execute beamforming; and a pressure wave tool apparatus located in either the drillstring or the wireline tool and coupled to the control circuit, the apparatus comprising: a tool body; and a plurality of pressure wave generators disposed around the tool body and configured to transmit a targeted pressure wave in response to the beamforming by the control circuit.
 16. The system of claim 15, wherein the control circuit is configured to control an amplitude and/or a phase of a signal transmitted from each antenna element such that the targeted pressure wave is at a frequency that avoids a resonant frequency of cement.
 17. The system of claim 15, wherein the plurality of pressure wave generators comprise a plurality of sound wave generators.
 18. The system of claim 15, wherein the plurality of pressure wave generators comprise a plurality of fluid wave generators.
 19. The system of claim 18, wherein the plurality of fluid wave generators are configured to vibrate a fluid at a frequency that is within a range of resonant frequencies of a formation.
 20. The system of claim 15, wherein a frequency of the targeted pressure wave is in a range of resonant frequencies of a target formation, wherein the range of resonant frequencies is determined based on wireline sonic logging tools or a microphone at a drill bit. 